linuxkpi: Conform to style(9) in atomic_dec_and_lock_irqsave()

[manu]

sys/compat/linuxkpi/common/include/linux/spinlock.h

169

The {} isn't needed for this block since you have only one line.

[nc]

Via email, @kbowling says that in style(9) "Values in return statements should be enclosed in parentheses."

[kbowling]

In D29998#673044, @nc wrote:

Via email, @kbowling says that in style(9) "Values in return statements should be enclosed in parentheses."

Note that this isn't a hard rule as some parts of the tree are less conformant than others. But in the previous review the parens were mentioned and this is what was meant.